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Conduction ppt

2.
Transfer of Thermal Energy
Thermal energy always flows
from a region of higher
temperature to a region of
lower temperature. Net flow
of thermal energy occurs
only when there is a
difference in temperature.

4.
Learning Outcome
At the end of this section, you should be able to:
• describe how energy transfer occurs in solids at the
molecular level.
Conduction

5.
Conduction
Conduction is the transfer of thermal energy through a
medium without any flow of the medium.
• Particles at the heated end
vibrate vigorously.
• They collide with neighboring
particles and transfer their
energy.
• Eventually the particles at the
cooler end are also set into
vigorous vibration.

6.
Conduction
Heat from the source as causing the atoms of the solid to
vibrate and gain kinetic energy.

7.
Conduction
These atoms cause neighbouring atoms to vibrate. Kinetic
energy is transferred from one atom to the next.

8.
Conduction
Heat energy is conducted through the solid in this way. As the
atoms of the solid gain kinetic energy the temperature of the
solid increases.

9.
Conduction in Metals
• In all solids, thermal energy is transferred through the vibration and
collision of particles.
• However, in metals, due to the presence of free electrons, thermal
energy is also spread through electron diffusion.
• Electrons gain kinetic energy and move more rapidly. They collide
with atoms in the cooler parts of the metal and pass on their energy
in the process.

10.
Conduction in Liquids and Gases
• Particles in liquids and gases are spaced farther apart those
in solids
• Collisions between particles occur less frequently; slow
transfer of kinetic energy
• Poor conductors of heat

14.
Convection
Convection is the transfer of thermal energy by means
of convection currents in a fluid (liquid or gas), due to a
difference in density.

15.
Conduction vs Convection
• In conduction, thermal energy is transferred from
one particle to another.
• In convection, thermal energy is transferred through
the actual movement of the heated particles from the
warmer to cooler parts of the fluid.

16.
Convection in Liquids
• When the water at the bottom of the
flask is heated, it expands.
• The expanded water is less dense than
the surrounding water and rises.
• Since the upper region is cooler, it is
denser and therefore sinks.
• The difference in the densities of water
in the different regions sets up a
convection current.
• This is shown by purple streams rising
from the bottom and sinking at the
sides.

17.
Convection in Gases
• When the air above the candle is
heated, it expands.
• The expanded air is less dense than
the surrounding air and rises out of
chimney B.
• Since the surrounding air is cooler, it is
denser and therefore sinks into
chimney A.
• The difference in the densities of the
air at the different chimneys sets up a
convection current.

19.
Land & Sea Breeze
• In the day, the land heats up faster than the
sea. The air above the land is heated,
expands and rises.
• Cool air above the sea is denser and moves
in to replace the warmer air. This sets up a
sea breeze.
• At night, the land cools faster than the sea.
• The air above the land is now cooler than the
air above the sea.
• A convection current is set up in the opposite
direction. This is called a land breeze.

20.
Radiation
Learning Objectives
• explain energy transfer of a body by radiation
• state the factors that affect the rate of energy
transfer by radiation

21.
Radiation
Radiation is the transfer of thermal energy in the form of
electromagnetic waves without the aid of a medium.
• All bodies emit infrared radiation
• Infrared radiation does not require a medium to be
transmitted. This is how the Earth is warmed by the Sun

23.
Effect of Colour and Texture onEmission
Rate of Infrared Radiation
Both tins are filled with
water, heated to the same
temperature and connected
to a data logger

24.
Effect of Colour and Texture onEmission
Rate of Infrared Absorption
The pieces of foil need to be
positioned at equal distances
from the source of heat in
order for the experiment to
be fair

25.
Other Factors affecting Rate of Infrared
Radiation Absorption/Emission
• Surface area
For two objects of identical mass and material, the object with the
larger surface area will emit or absorb infrared radiation at a higher
rate.
• Surface temperature
The higher the temperature of an object relative to its surrounding
temperature, the higher the rate of emission of infrared radiation.

26.
Applications of Transfer of Thermal
Energy
Learning Outcome
At the end of this section, you should be able to:
• describe how the concept of thermal energy transfer
by conduction, convection and radiation applies to
everyday life.

27.
Conductors
A material through which heat can move
easily is called a conductor.
Iron, silver, aluminum, stainless steel, and
copper are all examples of metals that are
good conductors.

28.
Insulators
A material that heat does not move through
easily is an insulator.
Plastic, wood, rubber, and glass are all good
insulators.
Many cooking utensils and handles are made
out of plastic, wood, or rubber.
Air is a good insulator.

32.
• Using the components given, explain how the vacuum flask manages
to keep the water at a steady temperature. If possible, also explain
how the material of the components affect the heat transfer.
Vacuum Flask

38.
• Using the components given, explain how the water system functions.
Household Water System

39.
A saucepan with a thick copper base contains water and is placed on a flat electric hot
plate.
(a)State the process by which thermal energy is
(i) transferred from the hot plate to the water;
(ii) transferred through the water.
(b)The sides of a saucepan are often polished, but the base is usually dark-coloured. Why is
this so?
Saucepan

40.
freezing unit
Refrigerator
• The freezing unit of the refrigerator is
placed at the top.
• Why this this the case? Draw arrows to
show the convection current within the
refrigerator

41.
What have we learnt today?
• How conductors and insulators can aid or reduce the rate of heat
trasnfer
• How conduction, convection and radiation can all play a part at the
same time to affect the transfer of heat

42.
Applications of Transfer of Thermal Energy
In your own groups, discuss
how the following
appliances would work!